The present invention relates to a novel pressure regulator, in particular to a back-pressure regulator, as well as to a process for regulating the pressure in a reactor system by using a pressure regulator in accordance with the present invention. The pressure regulator according to the present invention may be used to regulate normal pressure as well as back-pressure. In the text which follows, the term (back)-pressure regulator will sometimes be used to denote a pressure regulator capable of operating in either of these two modes.
It is well known in industry to operate plant processes under pressure, when it is desired to maintain components of the system at a certain pressure whilst a reaction is carried out. For example, in a hydrogenation process, high pressure hydrogen is available from a storage vessel at a pressure well above the working pressure required in the process. The flow of hydrogen emerging from the storage vessel, suitably a cylinder containing hydrogen under high pressure, say initially at 10 MPa (100 bar), is normally reduced to a lower value, say 1 MPa (10 bar), to prevent pressure waves being formed in the system. The flow can be fine-tuned to the actual flow needed in the reactor by means of a flow control valve. Such flow control valves will be referred to in the text which follows as pressure regulators. They can operate in a closed system or in a vented, one-phase system.
In order to keep the environment of the reactor vessel at the required pressure (for example 500 kPa (5 bar)), it is necessary to install a so-called back-pressure regulator downstream of the reactor environment. The back-pressure regulator must be capable of maintaining the pressure in the reactor at the required level. In practice, this means that the pressure regulator device must be capable of reducing or even closing off the passage of gas or liquid in a conduit downstream of the reactor until the pressure has returned to the required level. Conversely, the pressure regulator should also be capable of relieving the pressure by opening the conduit downstream of the reactor, to the extent required to return the pressure in the reactor vessel to the desired level by allowing passage of gas or liquid through the downstream conduit. A back-pressure regulator can also be used in systems which contain reactants, such as hydrogen, that will be consumed, or in systems in which higher pressures may be generated by the production of gases in the reaction, or due to the exothermicity of the subject reaction, causing the pressure to increase above the required level.
In some processes, the operator will be faced with a fluid containing both gaseous and liquid components, each contributing to the total pressure in the system. The partial pressures of the gaseous and liquid components will be dependent on the type of reaction(s) envisaged. In the context of this specification, the expression xe2x80x9cfluidxe2x80x9d will be used to denote materials either in the gaseous phase or in the liquid phase, or mixtures of the two phases, as the case may be.
A well-known problem in industry is that it is difficult to separate gaseous and liquid components in circumstances in which it is required to maintain the total pressure at a pre-determined level, especially in systems in which a multitude of vessels is involved, or when dealing with systems in which rather small volumes are present. One solution is to introduce a knock-out vessel in the conduit downstream of the reactor. This vessel can be equipped with a sluice system in order to drain off liquid. This allows the use of a standard gas-phase back-pressure regulator to deal with the setting of the pressure level of the gaseous components still present. In this respect, reference is made to U.S. Pat. Nos. 4,619,115; 4,682,622 and 4,971,104.
A plug valve is known from French Patent No. 1,237,237 which relies on annular seals for ensuring leak-tight cooperation between the valve and the cylindrical body which encloses it. The drawback of this known plug valve is that the seals are inevitably exposed to the fluids in the reactor stream and are susceptible to deterioration when contacted by aggressive chemicals.
Standard back-pressure regulators are operated by adjusting the flow through the conduit by increasing or decreasing the area through which the fluid travels by mechanical, pneumatic, electrical or any other means which is capable of adjusting the throughput to the required level. Systems based on springs or bellows may suitably be applied.
Turning now to systems which are designed to operate with small reactor volumes, typically operating with a throughput of 5 ml/minute or less, in particular systems operating under a flow regime of less than 0.5 ml/minute, it has been found that it is very difficult to control the back-pressure reliably, even for systems in which only one phase (either gaseous or liquid) is present. These difficulties are compounded for systems in which two phases (gaseous and liquid) are present. The option of introducing a knock-out sluice system is not possible in systems operating with such small reactor volumes because the size of the equipment is so small that fitting a vessel and a sluice device is no longer feasible. Morever, such systems suffer from the presence of so-called xe2x80x9cdead volumesxe2x80x9d which have a further disadvantage in that they cause significant dead time before the reaction products (or effluent) reach downstream analytical equipment. Moreover, dead volumes are prone to a build-up of sludge which hampers and eventually blocks the normal operation of the system. The proportion of xe2x80x9cdeadxe2x80x9d volume in relation to the xe2x80x9cactivexe2x80x9d volume increases as the trend towards more miniaturised systems is developed.
Morever, in systems using small reaction vessels and, in particular, in systems in which use is made of arrays of small reactors such as in the arrays currently envisaged for rapid catalyst screening, a number of additional problems need to be addressed. In particular, the consequences of operating at high temperatures (thermal expansion differentials) need to be taken into account. This, together with the high operating pressures that may be required, sets stringent requirements on the system in order to be able to operate in a leak-tight manner. Furthermore, in small reactor systems, small conduit systems will be used which are highly susceptible to external influences. This may have a significant effect on the process (or the screening) in actual operation. As mentioned above, the so-called xe2x80x9cdead volumexe2x80x9d which is nearly always present in valve systems becomes relatively large when down-scaling standard back-pressure regulators. This has an undesired influence on the working of the device.
It is therefore an object of the present invention to provide a pressure regulator which can overcome, or at least alleviate, the problems outlined above. It is also an object of the present invention to provide a pressure regulator which can operate in a single-phase and/or in a two-phase fluid system. It is a still further object of the invention to provide a pressure regulator which is self-regulating. It is yet another object of the invention to provide a pressure regulator which can operate as a normal pressure regulator and/or as a back-pressure regulator, depending on whether it is situated at a position upstream or downstream of the reactor vessel or any other part of the reactor system for which pressure regulation is required.
The invention is a fluid pressure regulator comprising a housing provided with an inlet and an outlet for fluids, a valve located movably inside the housing and provided with transport means to allow passage of fluids from an inlet side to an outlet side, a pressure setting means, and a passage in open communication between one of the inlet side, the outlet side or the transport means and a space enclosed by the housing and one end of the valve.
In particular, the present invention relates to a fluid back-pressure regulator which is placed downstream of the system through which it is intended to maintain a steady flow. The device is of particular use in a gas/liquid pressure environment which, hitherto, was impossible to control satisfactorily on a large scale, let alone on a small scale. The device is capable of operating reliably for a long time under severe reaction conditions, which is particularly advantageous when used in rapid screening duty for catalysts. Moreover, it can be manufactured at reasonable cost and enjoys operational robustness. In particular, the arrangement according to the present invention allows for chemical inertness in that there are no moving parts such as springs or O-rings exposed to the reaction environment and therefore susceptible to harm by aggressive chemicals. Most significantly, the pressure setting means can be isolated from the reaction environment, so the predetermined pressure at which the regulator actuates can be determined reliably because the pressure setting means will not be degraded by hazardous chemicals. The simplicity of the construction means that the pressure regulator according to the present invention is simple to machine and easy to assemble and dismantle. Maintenance is therefore straightforward and parts can be replaced easily, when required. Also, pressure regulators according to the present invention can be operated in such a manner that they are able to control a pressure difference, rather than absolute pressure. This increases sensitivity relative to many known devices.